CHAPTER 9 Biological Foundations of Personality

The Biological Tradition

Phineas Gage (1823-1860)

Temperament

 Individual differences in general mood or quality of emotional response that are moderately stable, inherited, and biologically based

Constitution of Temperament

The 4 humors (Melancholic, Choleric, Sanguine, Phlegmatic) Phrenology Body Types

Inhibited versus Uninhibited Children (Kagan, 1994)

Inhibited n  Reacts to unfamiliar

people and situations with avoidance, distress, restraint

n  Takes longer time to relax in new situations

n  Has more fears and phobias

n  Is timid and cautious

Uninhibited n  Reacts to unfamiliar

situations with spontaneity and joy

n  Takes shorter time to relax in new situations

n  Has fewer fears and phobias

n  Is not restrained in new situations

Kagan, Arcus, & Snidman (1993)

At 4-months, n  Videotaped behavior during familiar and

novel stimuli (voices, mobiles, balloons) n  Rated infants on reactivity (body movement,

crying)

At 14-months, 21-months, 4.5 years, 8 years n  Videotaped behavior and monitored

physiology

High vs. Low Reactive Infants (Kagan et al., 1993)

High reactive n  Show greater fearful

behavior, heart rate acceleration, increased blood pressure

n  Smiled and talked less with unfamiliar adult

n  Were shy with unfamiliar peer

n  Varied within group

Low reactive n  Showed lesser fearful

behavior, heart rate acceleration, increased blood pressure

n  Smiled and talked more with unfamiliar adult

n  Were less shy with unfamiliar peer

n  Varied within group

HEMISPHERE ACTIVATION

Left Hemisphere •  Approach-related emotion •  Arousal -> happiness, resilience in the face of stress •  Underarousal -> vulnerable to sadness and depression

Right Hemisphere •  Withdrawal-related emotion •  Arousal -> fear, disgust, anxiety •  Underarousal -> relaxation

Neurology and Freudian Defense Mechanisms

BRAIN PLASTICISTY

The story of Jody: A case of hemispherectomy

Behavioral Genetics

Different ways of estimating genetic influence:

Selective Breeding

Twin studies

Adoption studies

Heritability

Twin studies: Compare identical twins reared together with those reared apart Assume the similarity between “Together” twins due to shared genes and environment Assume the similarity between “Apart” twins due only to genes THEN: “Similarity of together” - “Similarity of Apart” = environment, and 1- environment = genes

Heritability

Another form of twin study: Compare monozygotic (MZ) together twins with dyzygotic (DZ) together twins Assume similarity of MZ due to genes and environment Assume similarity of DZ due to 1/2 genes and environment

Heritability

THEN:

Heritability = 2* (Similarity MZ - Similarity DZ) = 2*((genes + environment) - (1/2 genes +

environment)) = 2* (genes +environment - 1/2 genes - environment)

= 2*(genes - 1/2 genes) = 2*genes - genes = genes

Heritability

Heritability is an estimate of the percentage of the

variance in a particular characteristic in a particular

study that resulted from genetic variation in that

study.

Variance

Friendliness 0 5 10

* * * *

* * * * *

* *

* *

3 7

Variance = ((1-5)2 + (3-5)2 + (3-5)2 + ….. (10-5)2) / N-1 “ Average deviation”

HERITABILITY IS NOT

The chance that an individual will have a certain characteristic How much influence genes or environment have on an individual person The absolute influence of a gene outside the particular environment in which the estimate was made

Heritability is: an estimate of the percentage of the variance in a particular characteristic in a particular study that resulted from genetic variation in that study.

HERITABILITY

Some results from the major twin studies:

Intelligence – H = 30% - 70% (some specific cognitive abilities are more heritable than others) Activity level, emotional reactivity, sociability-shyness – H = 20% - 50% Neuroticism, extraversion, impulsivity, monotony avoidance – H = 23% - 45% Depression – H = 13% for male relatives and 30% for female relatives Vocational interests – H =0.43 Religiosity – H =0.49 Traditionalism – H =0.53 Attitudes toward drinking alcohol – H = 51% Radicalism and toughmindedness – H > 50% Aggressive, antisocial, criminal behavior – H about 50%

NATURE AND NURTURE INTERACTIONS

A Central Theme in Personality and Social Psychology

The dynamic interaction between the person and the situation. People come into the world with some predispositions. They act in accordance with these predispositions and get reactions and feedback from the environment. These reactions and feedback, in turn, inform, drive, and even determine their behavior in the future. The cycle continues.

Epigenetics Example

Oxytocin Receptor Polymorphism (rs53576) Gene and Culture Interaction

(Kim et al., 2011)

NATURE AND NURTURE INTERACTIONS

Diathesis-Stress Model

Examples Schizophrenia (genetic diathesis) Phobias (environmental diathesis) Alcoholism (possible genetic/environmental) Depression (possible genetic/environmental)

Stre

ss L

evel

Time

Critical Point

Patient Becomes Ill

NATURE AND NURTURE INTERACTIONS

Continuity of Behavior: Two Hypotheses (Caspi, Bem, & Elder, 1987)

The data on children who tantrum: Men: downward occupational mobility, erratic

work lives, more likely to divorce Women: married men with lower

occupational status, more likely to divorce, ill-tempered mothers

NATURE AND NURTURE INTERACTIONS

Continuity of Behavior: Two Hypotheses

Cumulative continuity n  We make certain choices, deliberate or not deliberate,

that determine what direction our life goes

Interactional continuity n  Early temperament forms an interactional style that

evokes reciprocal, maintaining responses from others. The person acts, the environment reacts, and the person reacts back.

MAIN POINTS ABOUT NATURE-NURTURE

Personality comes from a complex dynamic interaction of nature and nurture

Nature contributes to personality through genetics, as well as basic processes such as brain activation, temperment, neuroanatomy, and biochemistry.

Nurture contributes to personality through influences such as parental relationship, sibling competition, environmental stimulation, and culture.

Nature and nurture interact from the fetus throughout the life span. Diathesis, cumulative continuity, and interactional continuity are some of the mechanisms through which these interactions occur.